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The versatile 26-year-old sustained the problem in Chelsea's thrashing of Wigan earlier in August but he still asked his club that he be released to join his international team-mates.

Ivanovic, though, knew that he could not participate in their European qualifier against Faroe Islands on Friday or the match against Slovenia next Tuesday and he remains concerned that he could be sidelined until October.

"I asked Chelsea to let me come to Belgrade for a couple of days to spend some time with the team but I knew straight away I would be unfit to play," he told the Serbian Football Association's official website.

"There is a very slim chance I might recover for the Slovenia game but it is unlikely because the verdict is I could be out of action for up to six weeks."